CO2 is the best way I know of. I've seen "cervical dislocation" advocated by some, but if it's done wrong- like when someone's squeamish & not adept with that method- it's anything BUT humane, & personally I'd never try that either. No need to elaborate on the barbaric methods some people come up with.Before I got into snakes, I used to keep pet rats. Thanks for asking- it matters to most of us. Rats are intelligent & social creatures- they don't deserve cruel treatment, even if they're prey.